OBJECTIVES: a. Completion of histological material, including study of lymphoid system in the head tissues of the chickens under protein deficiency plus vitamin A deficiency. b. Extension of study of interferon in malnourished chickens subjected to NDV. c. Extension of electron microscopy of vitamin A deficiency to determine if mucus secretion differs from normal. d. Establish the sequence of early changes in the epithelial layer and determine if the appearance of a basal layer of cells interposed between the blood supply and the mucociliary epithelium is the cause of the degeneration of the latter. Determine also if the ciliated and the mucous cells disappear at the same time or if one precedes the other. e. Study the changes in the basal lamina and in the connective tissue, particularly in the cartilage. f. Determination of the effect of in vitro administration of vitamin A on the tissue cultures of nasal epithelium derived from deficient chicks. g. Testing the value of the mouse hepatitis system for the study of protein deficiency on cellullar susceptibility to this virus.